I recently was home for R&R from Iraq and had ordered a few parts for my motor. Problem was I ordered intake and other parts for a 302. Come to find out the car I had bought had a 351. I don't know what year motor it was, but I bought plugs for a 72 mustang with a 351, but when I brought them home they were too small. The motor is still using points, so its not new. Is there difference in spark plug size for different years? Is my first question. Second would I be able to order headers that will fit in there without altering the strut tower walls. I know the fit is really tight with the manifolds that already on there. It was kind of a pain ordering new parts, but it answered my question on why the car ran so well, thinking it was a 302 the whole time.
So you are figuring you have a 351w? A 72 Stang would have a 351c, so that might tell why the plugs didn't fit. Do you have any pics? Can you even get to the plugs? To answer one question directly, yes, Ford engines made a swap to smaller plugs depending on the year model, but that is not why your plugs didn't fit. You can use headers without shaving the towers, but it will be super tight fitting. Crites headers are probably your best bet, but even they require a small cut be made on the rib at the bottom of the tower. They give you a template with the headers I believe. Remember, the 351 has a different firing order than the old 302. Just a heads up for when you go to tune it up.
yea I found the firing order out the hard way. Was going off an old chilton manual, when I put a new cam in. The imprint on the top of the motor under the intake was 351w. I am guessing it was pulled out of an old truck. So with the headers I would still have to cut into the tower strut wall?
